This invention relates to a fuel injection system for an internal combustion engine, and more particularly a fuel injection system for feeding an internal combustion engine with fuel.
In order that an operation of an internal combustion is carried out while being kept optimum, it is essential to properly control an air-fuel ratio depending on a temperature at each of sections of the engine, an engine rotation speed and the like. A rate of injection of fuel fed to the engine by means of a fuel injector is determined depending on a fuel injection period or a period of time during which fuel is ejected from the injector and a pressure of fuel applied to the injector. The air-fuel ratio is affected by an ambient temperature and an atmospheric pressure, therefore, appropriate control of the air-fuel ratio requires to accurately control the fuel injection period based on control conditions such as an atmospheric pressure, a temperature of each of the sections of the engine, and the like.
For this purpose, a fuel injection system for an internal combustion engine is proposed which is constructed so as to control feed of a driving current to a fuel injector depending on an atmospheric pressure, an ambient temperature, a temperature of each of sections of the engine, an engine rotation speed, a degree of opening of a throttle and the like by means of a microcomputer, to thereby control a fuel injection period.
In the fuel injection system thus constructed, the microcomputer functions to carry out an operation of the fuel injection period suitable for starting of the engine at the time of starting of the engine. Upon completion of starting of the engine, the microcomputer carries out an operation of a fuel injection position or a rotation angle position at which fuel injection is started and the fuel injection period based on information on an atmospheric pressure, an ambient temperature and the like input thereto from a sensor and an output of a signal generator fed thereto, to thereby generate an injection command signal containing information on the fuel injection period obtained by the operation at the fuel injection position obtained by the operation. The injection command signal comprises, for example, a signal of a rectangular waveform rising at the fuel injection position and having a signal width equal to the fuel injection period. The injection command signal is then fed to an injector drive circuit, which then feeds the fuel injector with a driving current for a period of time during which the injection command signal is kept fed thereto. Thus, the injector keeps a valve provided therein open during feeding of the drive signal thereto, leading to injection of fuel.
When the internal combustion engine which has been subject to initial starting as described above is then temporarily stopped, followed by restarting, feeding of fuel to the engine at the same air-fuel ratio as in the initial starting causes the amount of fuel fed during the restarting to be excessive to a degree sufficient to cover an ignition plug, leading to a failure in restating of the engine. The term "initial starting" used herein indicates starting of an engine carried out after it is stopped for a long length of time and the term "restarting" referred to herein means starting of an engine carried out immediately or in a short period of time after it is temporarily stopped.
The above-described problem is solved by reducing a fuel feed rate at restarting of the engine. For this purpose, an fuel injection system for an internal combustion engine including a battery acting as a control power supply is proposed which is constructed so as to control changing-over of a fuel injection rate between initial starting of the engine and restarting thereof, as disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 41947/1992. A fuel injection system disclosed in the Japanese publication is adapted to obtain a residue of fuel in the engine when it is stopped by operation, so that a fuel injection rate at restarting of the engine is determined in view of the fuel residue obtained. Also, Japanese Patent Application Laid-Open Publication No. 221660/1990 discloses a fuel injection system for a two-cycle engine mounted thereon with a battery and started by means of a kick starter. The fuel injection system disclosed is adapted to reduce a fuel injection rate at restarting of the engine when the kick starter is operated. More specifically, the fuel injection system is constructed so as to count the number of times of kick operation of the kick starter, to thereby reduce a fuel injection rate in correspondence to an increase in counted value.
On the contrary, a conventional fuel injection system directed to an internal combustion engine free of a battery as disclosed in U.S. Pat. Nos. 5,216,994 and 5,161,496 is not constructed so as to carry out control for changing-over of a fuel injection rate between initial starting of the engine and restarting thereof. This is for the reason that when a microcomputer is operated using a generator driven by the engine as a power supply therefor, it starts a predetermined operation after a voltage of the generator is established; so that it fails to judge whether starting of the engine is initial starting of the engine or restarting thereof. Thus, the conventional fuel injection system in which the microcomputer is operated using the generator driven by the engine as a power supply therefor causes a fuel injection rate at the initial starting to be identical with that at the restarting, resulting in starting characteristics of the engine at the restarting to be significantly deteriorated.